1. Technical Field
Apparatuses and devices consistent with the present invention relate to a light emitting device module having a semiconductor light emitting device such as a light emitting diode (LED) and, more particularly, to a light emitting device module for improving heat radiation performance of the light emitting device.
2. Related Art
Recently, a lamp using a light emitting device such as an LED as a light source of the lamp instead of an incandescent lamp or a discharge bulb has been proposed. Previously, an LED has been applied to vehicle tail lamps and the turn signal lamps up to now. However, with the development of a white LED with a high intensity in recent years, the LED has been proposed as a light source for a vehicle headlamp. In this case, the LED generates heat accompanying the light emission, and thus the LED causes thermal runaway due to this heat, and the light emission characteristic is degraded. In particular, it is advantageous to select an LED with a high luminous intensity as the lamp for the vehicle, and the amount of heat generated by the LED is extremely large.
Japanese Patent Application Publication No. 2005-209538 describes an LED module having such a structure that a chip-shaped LED is mounted on a submount. The LED is covered with a dome-like lens, and the submount is mounted on a heat radiating plate to constitute the light source. The heat generated in the LED module is radiated via the heat radiating plate to prevent a temperature rise of the LED. However, since the submount is formed of a high-resistive insulating material in this structure, it becomes difficult to transfer the heat generated by the LED to the submount and also to transfer the heat from the submount to the heat radiating plate.
Japanese Patent Application Publication No. 2006-114820 describes another related art LED module. As shown in FIG. 9, in the related art LED module, a first LED 111 and a second LED 112 are connected electrically in series, and a plurality of front surface electrodes 122 (122p, 122r, 122n) used to mount the LED are formed on a submount 12 made of the high resistive member. In other words, a positive surface electrode 122p and a negative surface electrode 122n, which are used to feed an electric power from the outside and a relay surface electrode 122r, which is used to connect the first and second LEDs 111, 112 in series, are formed. A plurality of back surface electrodes 123 comprising a positive back surface electrode 123p and a negative back surface electrode 123n, which are connected electrically to the positive surface electrode 122p and the negative surface electrode 122n via through electrodes 124 (124p, 124n) respectively, are formed on a back surface of the submount 12. Also, in the structure in FIG. 9, a high heat-radiant substrate 13 made of a high heat-radiant member on which the submount 12 is mounted and which has a high heat radiating property is provided. A positive circuit electrode 132p and a negative circuit electrode 132n, which are connected electrically to the positive back surface electrode 123p and the negative back surface electrode 123n on the submount 12 respectively, are formed on a surface of the high heat-radiant substrate 13. Then, the LEDs 111, 112 are mounted on respective surface electrodes 122p, 122r, 122n of the submount 12 via bump electrodes Bp, Bn, and these LEDs are sealed with a translucent resin 15. The back surface electrodes 123p, 123n are bonded to the circuit electrodes 132p, 132n of the high heat-radiant substrate 13 by a metal brazing material 14 respectively. In this LED module, although not shown, the LED light source is constructed by securing a dome-like lens to the surface of the high heat-radiant substrate 13 to cover the LEDs 111, 112 in such a manner that the light generated by the LEDs 111, 112 is converged and emitted.
Then, the back surface of the high heat-radiant substrate 13 of the related art LED module is mounted on the heat radiating plate made of a metal, or the like. Therefore, the heat generated by the LEDs 111, 112 is transferred to the back surface electrode 123 from the surface electrodes 122 of the submount 12 via the through electrodes 124, then to the circuit electrodes 132 of the high heat-radiant substrate 13 from the back surface electrode 123. The heat is then spread to the overall high heat-radiant substrate 13 and transferred to the heat radiating plate. As a result, an improvement in the effect of heat radiation can be expected.
However, the related art LED module shown in FIG. 9 has some disadvantages. Since the relay surface electrode 122r, which is used to connect the first and second LEDs 111, 112 in series, out of the surface electrodes 122 of the submount 12 need not be connected electrically to the circuit electrodes 132 of the high heat-radiant substrate 13, the through electrodes 124 and the back surface electrode 123 are not formed in and on the relay surface electrode 122r. However, a part of heat generated by the first and second LEDs 111, 112 is transferred to the relay surface electrode 122r. Thus, in the related art LED module, this part of the heat is not transferred to the back surface side of the submount 12. Accordingly, the heat transfer to the high heat-radiant substrate 13 from the relay surface electrode 122r and, consequently, the heat radiated from the relay surface electrode 122r are very small. Therefore, it is difficult to transmit the heat generated by the LEDs to the high heat-radiant substrate at a high efficiency, and as a result the heat radiated is reduced, and it is difficult to improve the heat radiation. As an alternative, the respective areas of the submount and the high heat-radiant substrate may be increased in size in order to increase the amount of heat radiated. However, this increase in size also increases the overall size of the LED module. Thus, it is difficult to implement a small-sized light source or a small-sized vehicle lamp.